The invention relates to a device for locking the end positions of movable switch parts and, in particular, movable cross frogs, in which two relatively axially displaceable parts are capable of being displaced into a position coupled with each other in a positive or positive and force-transmitting manner in at least one direction of movement, wherein the relatively displaceable parts are comprised of a tube and a rod guided within the tube and are at least partially arranged in a stationary outer tube and the locking members cooperate with the relatively axially displaceable parts and the outer tube and are capable of being displaced in the radial direction into a locking position in a recess or inner annular groove of the outer tube.
From EP-A 603 156 B1, such a device for locking movable switch parts has already become known, in which the relatively displaceable parts are formed by a tube and a pin guided within the tube, and the locking members are designed as balls or rolls capable of being displaced in the radial direction. Departing from such a device, AT 405 925 B proposed to mount the balls in an expandable ring, or ring comprised of segments. The ring or ring segments constituted some kind of ball cage, allowing for the absorption of high locking forces without premature functional impairment. While balls in the idealized form, in principle, provide but a point contact thus causing a relatively high surface pressure, the cage constituted by the ring, or by the ring segments, in the outwardly displaced locking position provides a surface contact, via which high forces can be taken up as locking forces without any premature deformation or destruction. Such a configuration, however, involves the drawback that its assembly is relatively complicated, because the balls have to be held in an appropriate position during installation before being retained in the respective recess by the resilient ring, or the ring segments held together by springs, in a manner immersed in a rod guided within the tube. Enhanced force absorption, however, is only feasible in the locking position in the axial direction, and in the event of high switching forces the risk of damage to the balls as well as the rod via which the ring segments are displaced into their outer locking position continues to exist unchanged.